The invention relates to the field of turbomachines, particularly turbojet engines, and applies to stator vanes positioned within a compressor.
It relates more precisely to a novel reworking of a geometric shape of the vane in order locally to reduce the stress levels.
In the remainder of the description, the terms “upstream” or “downstream” will be used to denote the positions of the structural elements in relation to one another in the axial direction, taking the gas flow direction as reference point. Likewise, the terms “internal” or “radially internal” and “external” or “radially external” will be used to denote the positions of the structural elements in relation to one another in the radial direction, taking the axis of rotation of the turbomachine as reference point.
A turbomachine comprises one or more compressors delivering pressurized air to a combustion chamber where the air is mixed with fuel an ignited so as to generate hot combustion gases. These gases flow down-stream of the chamber toward one or more turbines which convert the energy thus received in order to rotate the compressor or compressors and thus provide the work required, for example, to power an aircraft.
A compressor, for example a high-pressure compressor, is made up of one or more compression stages each comprising a cascade of fixed vanes, followed by a rotor disk equipped with rotor blades. The cascade of fixed vanes, also known as the stator cascade, may be made up of a collection of angular stator sections, an example of which is illustrated in FIG. 1, each section 1 comprising a plurality of fixed vanes 2 connected by their internal end to an inner shroud 3 and by their external end to an outer shroud 4. The purpose of the stator sections is to straighten the stream of air arriving from the upstream side of the engine in order that this stream arrives on the upstream side of the rotor disk at an appropriate angle.
The vanes 2 are defined by two flanks known respectively as the pressure face 8 and the suction face 9 which form an aerodynamic profile with a leading edge and a trailing edge. The leading edge 6, or LE, is formed where the pressure face and the suction face meet on the upstream side. The trailing edge 7, or TE, is formed where the pressure face and the suction face meet on the downstream side. This aerodynamic profile is very important because it allows the vane to straighten the air stream arriving from the upstream side of the turbomachine as desired. This profile is designed by calculation and represented in the form of radial sections, taken along the vane stacking axis denoted E in the figure, at various heights with respect to the engine axis. The vane formed by these various radial sections is then incorporated between the inner and outer shrouds. The connection between the vane and the shrouds may be made in different ways. The vane and the shrouds may then be assembled by brazing.
For certain aerodynamic profiles, the radius of curvature of the TE is so small, for example of the order of one tenth of a millimeter that this, while the engine is running, leads to an increase in the static stress in the brazed joint between the vane and the outer shroud, on the pressure face side, toward the TE.
The stress level thus reached may prove prohibitive and cause cracks to appear in the joint.
When this type of crack appears, it is known practice for the geometry of the vane to be reworked with a view to reducing the stress level in the cracked zone. This reworking of known type is achieved by increasing the thickness of the vane over all the radial sections and for all or part of the height h of the vane. This type of reworking therefore alters the aerodynamic profile of the vane which means that a new profile needs to be calculated and the mechanical integrity of the new vane, particularly the level of stress reached in the cracked zone, needs to be verified. Several iterations between the aerodynamic engineering and the mechanical engineering are often needed in order to obtain a profile that is satisfactory both from an aerodynamic standpoint and from a mechanical standpoint. This type of modification is cumbersome to perform, lengthy and expensive. In addition, it entails a complete change of vane and has a very great impact on its manufacture.